This invention is directed to a needle for glaucoma surgery. More particularly, the invention is directed to a glaucoma needle which combines the operations of goniopuncture with that of sclera cautery for perpetuating a fistula in the sclera of the eye.
Glaucoma is a condition in which the intraocular pressure is elevated to the point that the optic nerve at the back of the eye suffers damage. Glaucoma is occasionally congenital, rarely juvenile, and commonly a disease of the older patient. There are two basic methods of treating glaucoma. One method is to reduce the intraocular pressure using drugs and another is to form a permanent puncture in the sclera of the eyeball using a surgical instrument or a laser. The sclera, the white tough outer coat of the eye is composed primarily of the protein collagen. None of these treatments works all the time, even in combination.
Conventional filtration procedures that are used for most forms of glaucoma when non-surgical means of controlling the glaucoma have failed (eye drops, systemic medication, laser trabeculoplasty) include trephine, iridectomy with cautery and trabeculectomy. Cautery procedures utilize the properties of the protein collagen which primarily comprises the sclera or tough white outer coat of the eye. Collagen undergoes permanent shrinkage when exposed to the temperatures above about 80.degree. C.
In the 1950's Dr. Harold Scheie popularized a procedure for opening the conjunctiva externally, exposing the sclera at the limbus (the edge of the cornea), and alternately heating and cutting with the blade until the anterior chamber was opened. After a fistula was thus formed, the outer tissue (conjunctiva) was reapproximated with sutures. The result was a permanent fistula between the anterior chamber of the eye and the potential space between the sclera and the relatively loose outer tissue surrounding the eye (the conjunctiva and Tenon's capsule). However, if cautery is applied too vigorously near the suture line, an inadvertent filtration bleb is produced after any ocular surgery.
A second procedure, goniopuncture, was described by Dr. Scheie in the 1950's for use in congenital or juvenile glaucoma. In this procedure a very fine knife is passed through the clear cornea, across the anterior chamber to the opposite anterior chamber angle and then out at the limbus, creating a puncture through the sclera and allowing fluid to percolate out under the conjunctiva, to form a bleb. In this operation the conjunctiva itself is not perforated by the blade. This operation frequently failed and was successful only in young people (under 30 years of age). It had been theorized that young sclera is somewhat elastic and that poking a hole in it would allow it to retract spontaneously, maintaining a fistula for the formation of a filtration bleb. In older patients, the sclera is not so elastic and goniopuncture perforations heal without producing any lasting filtration. Nevertheless, the success rate of this operation is estimated at somewhat less than 50%, even in young people.
An additional disadvantage of all such filtration procedures is that they are performed ab externo and use up a considerable amount of the available limbus. About 60.degree. of limbus is used for any conventional filtration procedure. Since only the upper 180.degree. is favorable for filtration surgery, one can usually place only two conventional filtration procedures without comprising results in future procedures.
It is an objective of the disclosed invention to provide an instrument which will allow an operation to combine the best features of (1) cautery (which causes collagen to contract permanently thereby perpetuating a fistula), and (2) goniopuncture (which can be performed easily and relatively non-traumatically) using only a tiny amount of limbus (perhaps 5%), thereby allowing multiple repetition above the operation, if necessary.
It is the second objective of the disclosed invention to increase the success rate of glaucoma surgery.
It is the third objective to accomplish this operation by means of a very thin knife (less than one millimeter in diameter preferably) which can be heated to a temperature adequate to cause permanent shrinkage of the sclera at the point on the knife where the limbus is traversed.